This invention relates to a device for dressing grinding wheels which grind outer surfaces of workpieces.
In a grinding machine having a grinding wheel, abrasive grains on the surface of the grinding wheel tend to be lost during the grinding operation, thus reducing the capability of cutting the surface of a workpiece. For recovering the capability, the operative surface of the grinding wheel must be dressed periodically.
For instance, in a grinding machine for grinding a plurality of cams on a cam shaft, it is an ordinary practice that, each time when a predetermined number of cams are ground, the grinding wheel is corrected or dressed by removing a predetermined depth from the surface of the grinding wheel.
However, the condition of the surface of the grinding wheel to be dressed is not always same, but is varied depending on its diameter. When the diameter of the grinding wheel is large, the reduction or deterioration of the abrasive property of the grinding wheel is comparatively small. However, when the diameter of the grinding wheel is reduced, the reduction of the abrasive property of the wheel becomes significant. The reason for this is considered that when the diameter of a grinding wheel is small, the number of abrasive grains on the surface is also small, and hence the amount of work to be accomplished by one grain increases when the entire grinding wheel carries out a predetermined amount of work. Thus, the time interval or separation between successive dressings carried out on the grinding wheel is determined based on that having a minimum operable diameter, the surface condition of which is deteriorated in a shortest period. In this case, however, since the grinding wheel of a larger diameter is dressed in a comparatively short period regardless of the surface condition remaining a sufficient capability of grinding, there arises a difficulty of wasting the precious material of the grinding wheel and shortening the operational life of the same.
For obviating the above described difficulty, there has been proposed another procedure wherein the dressing time interval is varied in accordance with the diameter of the grinding wheel. For instance, when the diameter of a grinding wheel is still large, the time interval is so selected that the dressing is carried out every (n+1) workpieces ground, whereas when the diameter of the grinding wheel is reduced, the dressing is carried out every n or (n-1) workpieces having been ground by the grinding wheel. Such a procedure, however, has been found disadvantageous for a case where a plurality of cams on a cam shaft are successively ground by a grinding wheel which is to be dressed in the course of a grinding cycle, because a remarkable difference in the surface structure tends to be exhibited on the cams on the cam shaft.